Graphite has a layered crystalline structure and consists of carbon atoms arranged in regularly stacked layers of hexagonal lattices. Given the variations in the arrangement of the carbons atoms in each layer of hexagonal lattices, graphite comes in different forms. For example, hexagonal 2H graphite is characterized in that the second layer of lattices is rotated by 180 degrees in order to be positioned between the identical first and third layers of lattices. Rhombohedral 3R graphite is formed by rotating the second layer of lattices by 120 degrees, rotating the third layer of lattices by 240 degrees, wherein the first and fourth layers of lattices are identical. Regarding the application of the heterophase graphite, 3R graphite is similar to adamas in terms of the arrangement of carbon atoms in lattices; hence, 3R graphite can be easily converted into adamas to facilitate the synthesis of adamas from graphite. By contrast, it is difficult to convert 2H graphite into adamas; as a result, the conversion process must entail changing 2H graphite to 3R graphite, and then changing 3R graphite to adamas. Furthermore, 2H graphite features hexagonal lattices and thus surpasses 3R graphite in structural strength and heat conduction. Therefore, 2H graphite is applicable to substrates which are highly thermally conductive.
A conventional way to purify graphite involves grinding graphite until it becomes a fine powder, treating the powdered graphite with hydrofluoric acid, neutralizing the acid-treated powdered graphite with sodium hydroxide (NaOH), treating it with hydrochloric acid, and finally rinsing it with water. The conventional purification technique is intricate, consumes plenty of reagents, and incurs high costs. For instance, China patent CN1331048 discloses that a conventional method of purifying 3R graphite comprises a crushing step, an acid treatment step, a water rinsing step, a drying step, a grading step, and a packing step, and is characterized in that the acid treatment is a one-shot treatment performed on natural 3R graphite, using a solution of mixture of hydrofluoric acid and hydrochloric acid. China patents CN87103661 discloses separating 3R graphite and 2H graphite by a special solution because of a difference of 0.06˜0.08 in relative density between 3R graphite and 2H graphite and using, as a medium, a special solution similar to graphite in relative density to regulate heavy-liquid temperature so that its relative density falls between the relative densities of 2H graphite and 3R graphite and thereby allow 2H graphite to ascend and 3R graphite to descend so as to effectuate separation; but the aforesaid process and subsequent solution treatment are intricate.
Therefore, it is necessary to provide a method of producing heterophase graphite to circumvent the crushing, oxidation, and acid-rinsing steps and thereby directly produce lumpy (sheetlike, crushed, particulate, and powderlike) 2H graphite and 3R graphite with a view to meet both efficiency requirement and green requirement and producing 2H graphite and 3R graphite that meets industrial needs.